Baptism is more than a sign as it is a sacrament, as it conveys the grace it symbolizes. Baptism's effect is the remission of original and actual sin. All have original sin save the Lord and His Mother. Actual sin is committed by those who have reached the age of reason and beyond.
But the text in Luke 18:15 says, "Now they were bringing even infants to him" (Greek, Prosepheron de auto kai ta brepha). The Greek word brepha means "infants"—children who are quite unable to approach Christ on their own and who could not possibly make a conscious decision to "accept Jesus as their personal Lord and Savior."2
As an aside, you should note that St. Paul wasn’t all gung-ho on circumcision. Some were looking to it in a legalistic way, and so Paul in exasperation told them they should just go ahead an emasculate themselves if they want to prove their super-spirituality. Reminds us how gritty the early Christians were .
Timothy was circumcised by St. Paul and there is no note of him doing it reluctantly. Secondly, my note of circumcision is in comparison to Baptism. The Old Covenant required circumcision for inclusion in God's people, the Jews, infants included. The New Covenant requires Baptism for inclusion into God's kingdom, all Jews and Gentiles, everyone, infants included.
Yes, Luke 18:15 says, “Now they were bringing even infants to him.” Jesus is happy to welcome adult and child alike.
Of course, that’s totally irrelevant here in a conversation about baptism.
Never mind, frogjerk. It’s clear your faith in Roman Catholic teaching (e.g., your statement that Jesus mother was free of original sin) is all-pervasive, and that no amount of biblical reasoning will be of any effect.